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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Inelastic collisions near Feshbach resonances in ultra-cold 7Li

Noam Gross, Zav Shotan, Lev Khaykovich

Published Jun 1, 2009• 0 citations
Publisher

Abstract

This study investigates two- and three-body losses in the vicinity of two Feshbach resonances on the |F=1,mF=0> state. The successful achievement of inelastic processes in ultracold 7Li Bose Einstein condensate near the Feshbach resonances is reported in detail. This investigation reveals that inelastic collisions are very strong in-between the resonances, despite the presence of zero crossing point where scattering length disappears.

DOI
10.1109/cleoe-eqec.2009.5194133

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In this thesis we explore ultracold atomic collisions in the vicinity of a magnetic Feshbach resonance located at 9.1 G, between 87Rb atoms in the |F = 2, mF = 1> and the |F =1, mF = 1> hyperfine states. We experimentally investigate the energy dependence of the enhancement of inelastic interaction in the neighborhood of this Feshbach resonance by analyzing the temperature dependence of a loss spectroscopy feature. An asymmetric widening of the resonance feature with respect to temperature is observed. We develop a simple model which captures these asymmetric line shapes through thermal averaging over the collision energy dependence of the Feshbach resonance. The energy dependence of the Feshbach interactions is further explored by colliding ultracold atomic samples at a fixed energy significantly above threshold using an optical trapping system; the elastic scattering enhancement analyzed by colliding the samples in free space, while for the inelastic measurements the collisions were carried out in trap. No conclusive resonant behavior could obtained for the elastic component of the 9.1 G resonance, however the inelastic scattering enhancement exhibited an anticipated shift.

•Jan 1, 2016•1 citation
This study investigates two- and three-body losses in the vicinity of two Feshbach resonances on the |F=1,mF=0> state. The successful achievement of inelastic processes in ultracold 7Li Bose Einstein condensate near the Feshbach resonances is reported in detail. This investigation reveals that inelastic collisions are very strong in-between the resonances, despite the presence of zero crossing point where scattering length disappears.
The properties of Bose-Einstein condensed gases can be strongly altered by tuning the external magnetic field near a Feshbach resonance. Feshbach resonances affect elastic collisions and lead to the observed modification of the scattering length. However, as we report here, the observed rate of inelastic collisions was strongly enhanced in a sodium Bose-Einstein condensate when the scattering length was tuned to both larger or smaller values than the off-resonant value. These strong losses impose severe limitations for using Feshbach resonances to tune the properties of Bose-Einstein condensates.
We study ultracold three-body collisions of bosons and fermions when the interatomic interaction is tuned near a narrow Feshbach resonance. We show that the width of the resonance has a substantial impact on the collisional properties of ultracold gases in the strongly interacting regime. From our numerical and analytical analyses, we identify universal features dependent on the resonance width. Remarkably, we find that all inelastic processes near narrow resonances leading to deeply bound states in bosonic systems are suppressed, while those for fermionic systems are enhanced. As a result, narrow resonances present a scenario that is the reverse of that found for broad resonances, opening up the possibility of creating stable samples of ultracold bosonic gases with large scattering lengths.
In the absence of inelastic scattering, Feshbach resonances produce poles in scattering lengths and very large peaks in elastic cross-sections. However, inelastic scattering removes the poles. Whenever the resonant state is coupled comparably to the elastic and inelastic channels, the scattering length exhibits only a small oscillation and peaks in cross-sections are significantly suppressed. A resonant scattering length is defined to characterize the amplitude of the oscillation, and is shown to be small for many collisions of ultracold molecules. The results suggest that cross-sections for some ultracold collision processes will be much less sensitive to details of the potential than has been expected.
Due to atomic interactions, a dilute gas Bose-Einstein condensate acquires a self- energy proportional to the two-body scattering length a. This self-energy strongly influences the stability, formation rate, size and shape, collective excitations, and other properties of a condensate. For a given atomic species at zero magnetic field, the scattering length is fixed, and this had led to a rather limited range of interaction strengths in experiments. However, it has been predicted that a magnetically tunable Feshbach resonance could be used to strongly modify scattering lengths [1]. We have observed such a Feshbach resonance in collisions of ultracold 85Rb(f =2, mf=−2) atoms in a magnetic field B. From our measured resonance position and width, we infer that the scattering length a2,−2 for collisions of these atoms has the dispersive resonance form.
In this thesis we explore ultracold atomic collisions in the vicinity of a magnetic Feshbach resonance located at 9.1 G, between 87Rb atoms in the |F = 2, mF = 1> and the |F =1, mF = 1> hyperfine states. We experimentally investigate the energy dependence of the enhancement of inelastic interaction in the neighborhood of this Feshbach resonance by analyzing the temperature dependence of a loss spectroscopy feature. An asymmetric widening of the resonance feature with respect to temperature is observed. We develop a simple model which captures these asymmetric line shapes through thermal averaging over the collision energy dependence of the Feshbach resonance. The energy dependence of the Feshbach interactions is further explored by colliding ultracold atomic samples at a fixed energy significantly above threshold using an optical trapping system; the elastic scattering enhancement analyzed by colliding the samples in free space, while for the inelastic measurements the collisions were carried out in trap. No conclusive resonant behavior could obtained for the elastic component of the 9.1 G resonance, however the inelastic scattering enhancement exhibited an anticipated shift.